1. Field of the Invention
This invention generally relates to a displacement detection device and, more particularly, to a displacement detection device and a displacement detection method thereof that have a high tolerance to the working surface and a high accuracy of the displacement detection.
2. Description of the Related Art
Conventional optical mice generally include an image sensor and a processing unit. The image sensor is configured to acquire a plurality of images of a working surface at different time intervals. The processing unit compares the correlation between the images so as to calculate a displacement of the optical mice with respect to the working surface. A control unit is configured to relatively control the motion of a cursor shown on a display device according to the displacement outputted by the optical mice.
When an optical mouse is being operated upon a critical surface, because images acquired by the image sensor thereof do not have enough characteristic variation (e.g. a contrast variation or a gray level variation is too low), the processing unit is hardly able to obtain accurate displacement of the optical mouse with respect to the critical surface according to the correlation between acquired images. Therefore, the optical mouse might not able to accurately control the motion of a cursor shown on a display device by moving on the critical surface. In addition, when the optical mouse is at rest, the cursor jiggles (referred as rest jiggle herein) on the screen; and when the optical mouse is lifted from the working surface, the cursor also jiggles (referred as lift jiggle herein) on the screen.
Conventionally, the characteristic variation or the image quality of an image can be estimated by calculating a characteristic index thereof so as to determine whether an acquired image is suitable for being used to calculate a displacement. When the characteristic index of the images of a working surface acquired by the image sensor is smaller than a threshold value, it means that the optical mouse is not able to accurately control the motion of a cursor by moving on the working surface. However, the selection of the threshold value will determine a tolerance to the working surface of the optical mouse. If the threshold value is higher, although the cursor jiggle can be reduced, the working surface that the optical mouse is being operated upon needs to have more apparent characteristic variation such that a limitation to the working surface is also increased. If the threshold value is lower, although the limitation to the working surface acceptable to the optical mouse is decreased, the cursor jiggle becomes more apparent.
Accordingly, it is necessary to provide a displacement detection device and displacement detection method thereof that can simultaneously increase a tolerance to the working surface of the optical mouse and reduce the phenomena of rest jiggle and lift jiggle.